The present invention relates to a method of correcting gradation and color balance of a composite image.
In recent years, there has been increased use of various personal cards such as corporation ID cards with individual FIGURES or human photographs. One such card having an individual human photograph comprises a data indication sheet inside of a plastic frame sheet that is backed with a plastic core sheet and sandwiched between transparent plastic cover sheets.
As is disclosed in U.S. Pat. No. 4,712,909, entitled "CRT COMPOSITE IMAGE PRINTING METHOD AND APPARATUS". issued Dec. 15, 1987, a data indication sheet comprises a sheet of color photographic paper having an individual human color image thereon, a computer graphic color image such as a pattern or a company identification mark, and printed characters of personal data and so forth. These images and characters are composed electrically as video signals and displayed on a CRT as a visible composite image to which the color photographic paper is exposed. A human subject image can be provided either by directly taking an image of a human subject using a TV camera or by taking an image of a human subject image formed on a negative film or print and inputting it into a video printer in the form of video signals. On the other hand, computer graphic images (which are hereinafter referred to as CG images) are usually provided by using a digitizer and are recorded in the form of image signals in a diskette or the like.
For better composite images, images to be composed are subjected to gradation and/or color corrections before being composed. A gradation correction circuit is used to effect these corrections and includes look-up table memories carrying table data, one memory for each color, namely red, green and blue, in order to transform respective color image signals. As a color correction circuit, there are provided three look-up table memories and one adder for adding together outputs from each of the look-up tables for each of the three colors.
Conventionally, the same table data is applied to both of the human subject image and CG image of a composite image in order to make a correction. Because there is a difference in image characteristics between the CG image made artificially and the human subject image which is taken from a real human subject, if the same table data is applied to both of these images, it is hard to provide a print of the composite image of these images having both well corrected color balance and gradation.
Further, in the case of images of human subjects taken under different lighting conditions with the same TV camera, finished prints show different color balances and gradations. The same table data is applied to the human subject and CG images in order to improve mainly the color balance and gradation of the human subject image of the composite image according to the lighting conditions under which the human subject image is taken, the color balance of the CG image processed along with the human subject image will change.